water__________(boil) at 100 degrees celsius.
past simple, past perfect, simple past, ect.
2 Answers
The example sentences here may be of interest to you.
You realize that since your profile page does not mention your native tongue nor your proficiency with Spanish/English that your question should be assumed to be asking about English grammar (which none of us did, of course).
You should state which language's grammar that you are asking about. (or better yet, complete your profile page)
By the way your sentence is a 0 conditional, in case that you are interested. A statement that is always true. If you heat water to 100°C (at standard temperature and pressure) then it boils.
There is a whole section devoted to conjugation. click here type in any verb, and you get all the conjugations.